This invention concerns the design and construction of a lifting device with a telescopic pole which is at least partly of the strap lift type. The device can vertically displace a load over several meters. It consists of a telescopic pole that can be equipped, as needed, at the base, with a stand system and, at the top, with any system that will allow the load to be attached or handled.
Telescopic lifting devices already exist which comprise modules that slide vertically over each other and in which the movement of an upper module with respect to a lower module is obtained by one or several cables connecting up the modules. Extension of the system and vertical displacement of the load attached to the upper module are obtained by means of a tensile force exerted on the crank handle of a winch fixed to the outside of the lower module and the base of the device and to which the end of one of the cables is connected.
To meet safety standards, mechanical means must be provided to lock the modules in extended position and thus prevent accidents occurring, due to breaking of the cable, for example. Manual installation of mechanical locking systems, such as passing a pin through the module to be locked, presents a risk if the operator who wishes to remove the device forgets to deactivate the said locking system. The operator could also turn the crank handle, thus unwinding several dozen centimeters of cable, before realizing that the locking system has not been deactivated. The resulting cable slack can then get stuck inside the telescopic system and break causing the load to fall suddenly when the operator releases the mechanical locking system.
A winch-driven cable has the disadvantage of requiring a complex set of pulleys which generates a large amount of friction, requiring both additional effort on the part of the operator to lift the load and a much longer load lifting time. The cable is also exposed to a number of risks such as crushing, pinching and corrosion, which rapidly reduces its life time and requires costly regular maintenance operations. At the extreme, the cable can break and cause accidents.